Here's what you have to do to get DL seats online. This isn't pretty....

Setup your search, be sure to login, choose Dl as the carrier, put in the people and class of service. For the desired outbound date search to a DL hub. For the return date put in something a couple of months past the outbound date.

Pick the earliest outbound flight was well as the first of the day on the bogus return. See what the system gives you. There will be one of four things: Std. award RT, a split of Std. and the higher one, a RT at nothing but the high level, and finally a generic error screen about an error in pricing the itinerary. Why this fourth happens I have no idea, aren't all seats available at the high level?

If you have problems in getting the non-error screen to return, try chaning the date/time of your bogus return. If that is totally futile then try jiggling the outbound date/time. You have to do this until you get a non-error response back. Once you have a non-error response back, NOTE THE DATE/TIME OF THE BOGUS FLIGHT and be sure to use this over and over.

Go through all the dates/times you can do on the outbound to the DL hub, using the known good bogus return. Write down the results.

I think you can see where this is leading. Now, from that DL hub you just spent an hour searching flights TO, do the same thing as above, only this time from the hub to the final destination. Go through the entire process of the hub outbound flight, dummy return to the hub, blah blah blah. Write down the results.

Repeat for the return segments in the same exact manner.

Stupid, huh? Blame NW, their interface in showing DL flights is so horribly broken it is laughable. There are many flights that either don't show up at all or get the error screen, but when pieced together by legs it all comes together. The error screen is the big killer of this mess. If it would just show all the flights and the award level available you wouldn't have to go through all this, but for some reason they don't.